The present invention relates to a developer concentrate capable of dilution with tap water to a ready-to-use state with tap water, which concentrate is suitable for developing negative-working exposed reproduction layers having a protective top layer in copying materials, and also a process for producing printing forms.
Copying materials of the type mentioned are used, in particular, in producing printing plates or photoresists and are composed of a layer base and a negative-working, photosensitive reproduction layer which may contain diazonium salt polycondensation products and/or photopolymerizable compounds as photosensitive components. The layer bases used in these copying materials are made of metals such as zinc, chromium, copper, brass, steel, aluminum or combinations of these metals, plastic sheets, paper or similar materials. The layer bases may be coated with the photosensitive reproduction layer without a modifying pretreatment. Preferably, however, the layer bases are coated after carrying out a surface modification such as a mechanical, chemical or electrochemical roughening, an oxidation and/or a treatment with hydrophilizing agents (for example, in offset printing plate bases).
Known developers or developer mixtures suitable for these copying materials have, in particular, the following disadvantages:
they often contain fairly high proportions of organic solvents which should, if possible, no longer be present in modern developers for PA0 although lauryl sulfate or other alkyl sulfates or alkanesulfonates conventionally often used in practice are, per se, effective developer components for the specified photosensitive reproduction layers, they require a comparatively long development time, they foam too extensively in processing machines, in particular in the case of vertical development, and the solubility in water at low temperatures (for example, from about 10.degree. C. and lower) decreases to an extent such that, at autumn or Winter temperatures, flaky residues which are often troublesome for the processor may be produced in the stock solutions. Spots of grease and adhesive residues such as may occur in handling offset printing plates under practical conditions are removed by these developer components at best after a long action time and by additional mechanical aids; PA0 although the lauryl sulfates or other alkyl sulfates or alkanesulfonates are frequently also suitable when used for the specific PA0 they also are unsuitable in general for suppressing the impurities (flakes and filaments) which are encountered in many cases, mainly in mechanical development, and which settle as redeposits on the printing forms, with the result that optimum quality of the final product cannot be achieved, even when the developer is used for a long time. PA0 has a high solids content and also exhibits no precipitates, phase separations or turbidities on thawing even after a fortuitous freezing, PA0 can, if necessary, be diluted before use in the printing shop with water containing Ca and Mg ions, in particular tap water, to the extent necessary in practice without precipitates appearing in the process, PA0 develops rapidly and in doing so has equally ideal development properties (good resolution of the non-image areas and non-attack of the image areas) in order to enable it to be used in automatic processing systems, PA0 develops either as a concentrate or in the various degrees of dilution without flake and filament formation and at the same time has a high economy in use, i.e., can be used even over a prolonged period of time in its development capacity without forming contaminants, PA0 can be used either with binder-containing or with binder-free systems and PA0 is suitable for developing reproduction layers having a protective top layer.
ecological reasons such as a low boiling point, fire hazard, unpleasant smell, adverse effect on waste water and exhaust air and expensive precautions for eliminating the solvents after development;
reproduction layers for which they were developed and with which they are also successfully used in the respective examples, they exhibit more or less considerable difficulties with layers which are different from these specific reproduction layers, i.e., they cannot be employed universally.
U.S. Pat. No. 4,716,098 describes a developer mixture which is different from the prior art described above, does not exhibit the disadvantages thereof and is suitable for developing lithographic printing plates. The layers described therein include a diazonium salt polycondensation product and an alkali-soluble binder which contains carboxyl groups. The developer mixture is stable only in very dilute form and can therefore exist only in dilute aqueous solution. The developer described includes up to 85% water, as a result of which unnecessarily large containers which have adverse effects on transport and application are needed.